Artificial respiration system

ABSTRACT

Air is alternately forced into the lungs of a patient during an inhalation period and permitted to flow out of the lungs of the patient during a subsequent exhalation period. A synchronizing signal is generated indicative of the time intermediate the inhalation period and the exhalation period. A warning unit is provided for generating a warning signal. The pressure of air in the lungs of the patient is detected to determine whether or not such pressure falls below a predeterined value or overcomes a predetermined maximum value. If the detected pressure in the patient&#39;&#39;s lungs falls below or respectively overcomes such predetermined value during the time of generation of one of said synchronizing signals, that is, during the specific time period intermediate the inhalation and exhalation periods, then the warning unit generates a warning signal.

United States Patent Plicchi Apr. 15, 1975 ARTIFICIAL RESPIRATION SYSTEM3,645,133 2/1972 Simeth et al. 128/2.08 ux [76] Inventor: GianniPlicchi, Via Cimarosa 2, OTHER PUBLICATIONS Bologna, Italy The Lancet,Oct. 12, 1957, p. 725.

[22] Flled: 1973 Primary ExaminerKyle L. Howell PP 2, 29 Attorney,Agent, or FirmMichael S. Striker Related US. Application Data ABSTRACT[63] Continuation-in-part of Ser. No. 239,977, March 31,

1972, abandoned, A11 15 alternately forced Into the lungs of a pat1entdurlng an lnhalation period and permltted to flow out [30] ForeignApplication Priority Data of the lungs of the patient during asubsequent enhala- A r l 6 197] Ital 2325 5/71 t1on perlod. Asynchronizing signal 1s generated mdlcy ative of the time intermediatethe inhalation period U S Cl 128/2 l28/DIG 29, 128/145 8 and theexhalation period. A warning unit is provided [5 l A61b 6 for generatinga warning signal. The pressure of air in [58] Fie'ld R 145 5 the lungsof the patient is detected to determine "'i' 5 5 whether or not suchpressure falls below a predeterined value or overcomes a predeterminedmaximum References Cited value. If the detected pressure in the patientslungs falls below or respectively overcomes such predeter- UNITED STATESPATENTS mined value during the time of generation of one of 3,333,5848/1967 Andreason et al 128/1455 said synchronizing signals, that is,during the specific 3,414,896 6t al. X time period intermediate thginhalation and exhalation periods, then the warning unit generates awarning sigc oener e 1 3,603,955 9/1971 Levy 3,643,652 2/1972 Beltran128/208 9 Claims, 3 Drawing Figures PATENTEDAPR 1 5mm SHEET 1 23.877.467

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PATENTEDAPR 1 51975 SHEET 2 [If Em Q N QE lllllll'll'llllllllll.llllllilnll-lll'llnll'lllll'l] ARTIFICIAL RESPIRATION SYSTEMCROSS-REFERENCES TO RELATED APPLICATIONS The present application is acontinuation-in-part of my prior copending application Ser. No. 239,977,filed on Mar. 31, 1972, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to methods andsystems for the artificial respiration of a patient, and furthermorerelates to means and methods for determining insufficiency of theartificial respiration operation being performed.

It is known to operate mechanical respiration machines in such a manneras to blow gas into the lungs of a patient through a pipe inserted intothe patients trachea, thus expanding the patients chest by the pressureof the introduced respiration gas, and then permitting the patient toexhale. However, with the known techniques, it is possible that thepatients lungs may not be sufficiently ventilated, due for example to aleakage in a gas line, or due to an obstruction in one of the gas lines,or for other reasons. Simple measurement of the pressure of gasdelivered to the patient is not sufficient to indicate the ventilationcondition of the patients lungs, because it is possiblethat a properoperating pressure may be measured although the lungs are in fact notbeing properly ventilated. This could happen, for example, if there werean obstruction in the gas delivery line downstream of the point wherethe, gas pressure is measured. In the same manner it may be desirable tocontrol the pressure value into the patients lungs to limit it below amaximum value that could be dangerous for the patient.

SUMMARY OF THE INVENTION The present invention has for its object theprovision of a method and an apparatus for signalling insufficient lungventilation which avoids the above-mentioned disadvantage by measuringthe gas pressure during the interval between inhalation and exhalation,and by determining insufficient lung ventilation when the measured gaspressure at such time is less than a predetermined value. This resultsin a safer check, since the pressure measured at the end of theinhalation stage is more directly dependent upon the amount of gas blowninto the patients lungs.

This object, and others which will become more understandable from thefollowing description of a preferred embodiment, can be met, accordingto one advantageous concept of the invention by providing an artificialrespiration system which includes respirating means for alternatelyforcing air into the lungs of a patient during an inhalation period andpermitting outflow of air from the lungs of the patient during asubsequent exhalation period. Synchronizing means is provided forgenerating a synchronizing signal indicative of the time intermediatethe inhalation period and the exhalation period. Warning means isprovided for issuing a warning signal. Pressure-detecting means isprovided for detecting when the pressure of air in the lungs of thepatient falls below a predetermined value. Activating means is connectedto said synchronizing means for receipt of said synchronizing signal andis connected to said pressure-detecting means and is operative forcausing the warning means to issue a warning signal if the pressuredetected by the pressure-detecting means falls below the predeterminedvalue during the time of receipt by the activating means of saidsynchronizing signal.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 depicts an artificialrespiration system according to the invention;

FIG. 2 depicts in graphical form certainaspects of the operation of theartificial respiration system shown in FIG. 1; and

FIG. 3 depicts the structure of the schematically depicted respiratingunit 1 shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 depicts an automaticrespirating machine for respirating the lungs of a patient 2. A conduitfor air is inserted into the trachea of the patient 2, and has twobranches 3 and 4. The respirating machine pumps air into the patientslungs through inhalation conduit 3 during the inhalation period a (seeFIG. 2). The air pumped through inhalation conduit 3 expands thepatients chest, filling the lungs of the patient with air.

Subsequent to the inhalation period a, the pumping of air throughinhalation conduit 3 is terminated, and an exhalation conduit 4,previously blocked, is opened, permitting the air in the patients lungsto escape through conduit 4, and permitting the air pressure which hasbuilt up in the patients lungs to fall towards atmospheric pressure.Such exhalation is permitted to occur during the exhalation perioddesignated c in FIG. 2.

Intermediate the inhalation period a and the exhalation period c is ashort-lasting pause b, having a duration on the order of about 200/1000of a second. The time duration of pause b, relative to the timedurations of the inhalation period a and the exhalation period c, hasbeen greatly exaggerated in FIG. 2, for the sake of clarity.

One of the principal features of the invention is the determination ofthe pressure in the patients lungs during the short-lasting pause boccurring intermediate the inhalation period a and the exhalation periodc.

To this end, the respirating machine schematically depicted in FIG. 1generates, on synchronizing line 8, a pneumatic synchronizing signalcontemporaneously with the occurrence of the short-lasting pause b. Thepressure in the patients lung is monitored during this interval b and,if during the interval b the pressure of air in the patients lungs islower than a preselected minimum sufficient value, acoustical and/orvisual alarm signals will be issued.

The illustrated embodiment will now be described in greater detail.

FIG. 3 shows essential portions of the respirating machine 1. Inparticular, the machine 1 comprises two pneumatically controlled valves13 and 12. The valve 13 has an inlet 3' into which is pumped therespiration air to be pumped into the patients lungs. The valve 13 hasan outlet 3 which passes to the inlet of valve 12. Valve 13 can be madeto either permit air flow'from its inlet 3 to its outlet 3, or can bemade to block such air flow. The control of valve 13 is effected by theapplication thereto of pneumatic control signals, via a control line 19,in a manner described below.

The valve 12 is a three-port valve. In the first of the two positionsthereof, valve 12 permits the pressurized gas in inhalation pipe 3 toenter the lungs of the patient, during the inhalation phase a. In thesecond of the two positions thereof, valve 12 establishes communicationbetween the lungs of the patient and the exhalation pipe 4, to permitthe air under pressure in the patients lungs to flow out of the patientslungs through exhalation pipe 4, during the exhalation phase c. Thecontrol of valve 12 is effected by the application thereto of pneumaticcontrol signals, via a control line 29, in a manner described below.

The cyclical control of the valves 13 and 12, considered from a purelyfunctional point of view, is as follows:

During the inhalation phase a, the valves 13 and 12 are both opened.Accordingly, the ventialtion gas entering inlet conduit 3 passes throughvalve 13, through inhalation pipe 3, and through valve 12'into the lungsof the patient.

During the phase b, intermediate the inhalation phase a and theexhalation phase c, the valve 13 is closed and the valve 12 is in thefirst position thereof wherein it establishes communication between thelungs of the patient and the inhalation pipe 3. The pressure in theinhalation pipe 3 will now be established not by the action of the(non-illustrated) pressure-creating means connected to ventilation gasinlet 3; instead, the pressure in the inhalation pipe 3 will beestablished by reason of the pressure build-up in the lungs of thepatient and by reason of the compressive force exerted by the patientsthorax.

During the exhalation phase 0, the valve 13 is closed and the valve 12is in the position thereof wherein it establishes communication betweenthe interior of the patients lungs and the exhalation pipe 4, so thatthe pressure build-up in the patients lungs can be relieved by anoutflow of air through the exhalation pipe 4.

The means which establishes this sequence of valve openings and valveclosings is depicted in FIG. 3.

A pressure pulse generator 14 continuously generates a pneumaticsquare-wave comprised of pressure pulses having a pulse-duration equalto the duration of the inhalation phase a, but separated from each otherby a time interval d. The duration of the time interval d is equal tothe duration of the exhalation phase c plus the duration of theintermediate phase b (d b c). Evidently, the pulse-repetition frequencyof the pulse train generated by pulse generator 14 establishes therespiration frequency for the artificial respiration of the patient. Thegenerator 14 can, for example, comprise a source of pressure having anoutlet provided with a solenoid-operated valve, with the electricalinput of the solenoid-operated valve being connected to and controlledby an astable multivibrator having a first unstable state lasting a timeinte rval-corresponding to the duration of the inhalation phase a andhaving a second unstable state lasting a time interval corresponding tothe duration d.

The cycle of operation of the means which control the opening andclosing of the valves 12 and 12 will now be described.

INHALATION PHASE a The pressure pulse generated by pulse generator 14 istransmitted through control-pulse conduit 19 and is applied to thecontrol input of valve 13, thereby opening the valve 13. As a result,the valve 13 permits passage of pressurized gas from the inlet 3 thereofto the outlet 3 thereof.

That same pressure pulse generated by pulse generator 14 is furthermoretransmitted through conduit 30 to the upper chamber 284 of a pneumaticrepeater device 28, causing the valve member 287 thereof to assume itslowermost position, by reason of the pressure in chamber 284 exceedingthe normal biasing or operating pressure of 0.5 kg/cm established in thechamber 281 by way of biasing-pressure conduit 31. Once the valve member287 has been pushed in this manner to the lowermost position thereof, itunblocks the pressure inlet 282, which is connected to a pressure sourceof 1.4 kg/cm This pressure of 1.4 kg/cm passes in through the conduit282 and then out through the conduit 283, and then through thecontrol-pulse conduit 29 to the control input of the two-position valve12. When this 1.4 kg/cm control pulse is applied to the control input ofvalve 12, it causes valve 12 to assume the position thereof whereincommunication is established between the interior of the patients lungsand the inhalation pipe 3.

Thus, the valve 13 is in the open position thereof, and the valve 12 isin the position establishing communication between inhalation pipe 3 andthe interior of the patients lungs. Accordingly, the respiration gasintroduced into inlet 3 enters the patients lungs.

This situation prevails for the entire duration of the pressure pulse,i.e., for the entire duration of the inhalation phase a.

THE INTERMEDIATE PAUSE b At the end of the pressure pulse generated bypulse generator 14, the valve 13 reassumes its normal closed position.

Furthermore, at the end of the pressure pulse generated by pulsegenerator 14, the pressure established in chamber 284 or repeater 28terminates, and as a result the valve member 287 reassumes itsillustrated uppermost position. With valve member 287 in its illustratedposition, theinlet 282 is blocked, and the 1.4 kg/cm valve-controlpressure cannot pass into the conduit 282 and out the conduit 282 andthrough the conduit 29 to the control inlet of the valve 12 to maintainthe latter in the first position thereof. However, as will be clear fromthe foregoing functional description of the operation of valve 12, valve12 must be maintained in its first position (establishing communicationbetween inhalation pipe 3 and the interior of the patients lungs) duringthe intermediate pause b. The valve 12 is maintained in the firstposition thereof in the following manner.

. Immediately upon termination of the pressure pulse a generated bypulse generator 14, a pulse having a pulse-duration of for example200/1000 sec. is transmitted through the inlet 235 of repeater 28, thenthrough the outlet 28o, then through the control-pulse conduit 29, tothe control input of valve 12, thereby maintaining valve 12 in its firstposition for an additional 200/1000 sec. subsequent to the terminationof the inhalation phase a. The means for generating this supplementalpulse having a pulse-duration of for example 200/1000 sec. will bedescribed below.

During this 200/1000 sec. time interval, the valve 13 is in closedposition, and the valve 12 is in the first position thereof, i.e., inthe position thereof wherein it establishes communication between theinterior of the patients lungs and the inhalation conduit 3. Clearly,the pressure now prevailing in the inhalation conduit 3 will be dueexclusively to the pressure build-up in the patients lungs and thecompressive force of the patients thorax. This pressure is applied to apressuremonitoring device 26, via a communication conduit 3". In amanner described in detail below, the pressuremonitoring device 26evaluates the pressure prevailing in the patient s lungs during thispause period b, and determines whether it is within an acceptable range.In the event that the pressure just mentioned is not within suchacceptable range a warning signal is generated.

The construction and operation of the pressuremonitoring device 26 ofFIG. 3 will be explained in detail below. However, it is noted now thatpressuremonitoring device 26 is operative to monitor the pressure in thepatients lungs specifically during the pause period b. To this end,pressure-monitoring device 26 is adapted to receive a synchronizingpulse, via the illustrated second inlet conduit 8 thereof. Thissynchronizing pulse has a pulse-duration equal to the duration of theintermediate pause period b. As a result, pressuremonitoring device 26is informed of the fact that the intermediate pause period b isoccurring and that the pressure in the patients lungs should at thistime be evaluated.

THE EXHALATION PERIOD 0 The aforementioned pulse having a duration of200/1000 sec. and applied to control-pulse line 29 via repeater inlet285 and repeater outlet 286 terminates, and the exhalation period ccommences. Specifically, upon termination of the 200/1000 sec.supplemental pulse, the valve 12 reassumes its normal position whereinit establishes communication between the interior of the patients lungsand the exhalation conduit 4. Accordingly, the pressure build-up in thepatients lungs is relieved through the exhalation conduit 4, and thepatients thorax sinks in an exhaling manner.

. THE GENERATION OF THE PULSE CORRESPONDING TO PAUSE b The pulse traingenerated by pulse generator 14 is applied to the input conduit 14 of apneumatic inverter device 16. Inverter 16 essentially is operative forproducing at its outlet 18 a pressure pulse train inverted with respectto that generated by pulse generator 14. In other words, the inverter 16produces at its outlet 18 a pressure pulse of duration d during the timeinterval between the pressure pulses produced by generator 14.

Inverter device 16 performs this function as as follows. Inverter 16receives a biasing or operating pressure of 0.5 kg/cm via a biasingconduit 17. This 0.5 kg/cm biasing pressure tends to move the valvemember 161 of inverter 16 to the lowermost position thereof. A pressureof 1.4 kg/cm is applied to the inlet 163 of the inverter 16. However,when the valve member 161 is in the illustrated uppermost positionthereof,

the inlet 163 is blocked off. Valve member 161 will be in such blockinguppermost position during the existence of each pressure pulse generatedby pulse generator 14. This is because the pressure pulse generated bygenerator 14 is applied to the inlet 15 of inverter 16 and enters thecompartment 166 and overcomes the biasing pressure force of 0.5 kg/cmapplied via biasing conduit 17, to thereby move the valve member 161 toits illustrated blocking position.

However, during the time intervals d intermediate the pulses generatedby pulse generator 14, no pressure in compartment 166 opposes the 0.5kg/cm biasing pressure applied via conduit 17, and accordingly valvemember 161 moves to its lowermost, or unblocking position. As a result,the 1.4 kg/c m pressure applied to inlet 163 will pass out throughoutlet 164 in the form of a pressure pulse of time duration d in conduit18.

Inasmuch as device 16 produces at its outlet 18 pulses contemporaneouswith the intervals between the pulses generated by pulse generator 14,device 16 has been referred to herein as an inverter. It is tobe-understood that a pulse appears at the output 18 of inverter 16 assoon as a pulse generated by pulse generator 14 ends.

The signal on inverter outlet 18 is applied simultaneously to conduits20, 23 and 27.

The conduit 18 feeds this pressure pulse to the inlet 211 of a furtherpneumatic device 21. Device 21 is biased towards the lowermost positionthereof by the action of a 0.5 kg/cm biasing pressure applied tocompartment 215 thereof by way of biasing pressure conduit 17'. Theaction of this biasing pressure is to normally maintain the valve member214 of device 21 in the lowermost position thereof. As a result, thesignal applied to inlet 211 passes out through outlet 212, and reachesconduit 24.

The same signal, i.e., the pulse appearing at output 18 of inverter 16,as mentioned before, is also applied to conduit 23. However, conduit 23includes a manually adjustable throttling valve 22. The conduit 23 leadsinto the compartment 213 of the device 21. When the 1.4 kg/cm pressurepulse appears at the outlet 18 of inverter 16, this pressure istransmitted 'via conduit 23 to the compartment 213 of device 21, but notinstantaneously. Instead, there is a gradual build-up of the pressure incompartment 213 to the value 1.4 kglcm the gradualness of the build-upresulting from the provision of the throttle valve 22 in conduit 23.

When the pressure iscompartment 213 has risen to the 1.4 kg/cm value,after the exemplary time delay of 200/1000 sec., the pressure incompartment 213 overcomes the biasing pressure in compartment 215,causing the valve body 214 to move to its illustrated uppermostposition. As a result, the pressure established via conduit 20 in inlet211 of device 21 can no longer be communicated to the outlet 212thereof. Accordingly, the duration of the 1 .4 kg/cm pressure pulseappearing at outlet 212 of device 21 will be equal to 200/1000 sec., inthe illustrated embodiment, namely the duration of the intermediatepause b.

Finally, as mentioned above, the 1.4 kg/cm pressure pulse appearing atthe outlet 18 of inverter 16 is also applied to conduit 27 andtherealong to the compartment 251 of the pneumatic device 25. A biasingpressure of 0.5 kg/cm is maintained in the compartment 254 of the device25. This biasing pressure normally maintains the valve member 253 in thelowermost posion thereof. However, when the 1.4 kg/cm pulse apears atoutlet 18 of inverter 16, and is applied via conuit 27 to compartment251, the pressure in compartient 251 overcomes the pressure incompartment 254, nd as a result the valve member 253 moves to itsillusrated uppermost position. This closes the inlet 252 ommunicatingwith the aforedescribed conduit 23. As

result, the pressure in the conduit 23 cannot be reeved through theoutlet 255. However, when the 1.4 vg/cm pressure established incompartment 251 is terninated, the 0.5 kg/cm biasing pressure incompart- Jent 254 moves the valve member 253 to its lower- .lOStposition, and the pressure in conduit 23 can be re- .eved through outlet255.

It will be clear that the purpose of providing relief deice 25 is toensure that pressure cannot build up in ompartment 213 of bistabledevice 21 except during he time interval d between two successive pulsesgenrated by pulse generator 14.

As a result of all of the foregoing, a synchronizing iressure pulse of200/1000 sec. duration is applied to he synchronizing inlet 8 ofpressure-monitoring device 56 at the same time that the pressure appliedto the nlet 3" of device 26 is at a value corresponding to the iressurein the patients lungs during the brief pause b ntermediate theinhalation and exhalation phases.

The construction and operation of the pressurenonitoring device 26 ofFIG. 3 will be explained with eference to FIGS. 1 and 2.

The many components and connections depicted in IG. 3, except for theschematically shown box in FIG. i, all correspond to the components 1,3", 3 and 4 of *IG. 1. In FIG. 1, reference numeral 1 generallydesigiates the respiration machine shown in FIG. 3, with the nhalationand exhalation conduits 3 and 4 being shown .omewhat more schematically.The remaining compoients in FIG. 1 correspond to the pressure-monitoringlevice 26 in FIG. 3.

The pressure-monitoring arrangement of FIG. 1 in- :ludes a pressuremeter generally designated by refer- :nce numeral 5. The pressure meter5 comprises a flexble diaphragm 51 which is pre-loaded by means of a:crew 52, so that it will become deformed in a predeternined manner whenthe pressure entering chamber 53, ia conduit 3" explained with referenceto FIG. 3, ex- :eeds a predetermined minimum value. It is noted that lpressure corresponding to the pressure in the paients lungs is appliedvia conduit 3" to compartment 53 of pressure meter 5 not only during thepause period 7 but also during the inhalation period a, in the illustra-.ive embodiment.

The diaphragm 51 is mechanically coupled (as repreiented by the brokenlines) to a resilient shutter mem- Jer 61. When the pressure incompartment 53 exceeds 1 predetermined minimum value, the diaphragm 51noves towards the right, causing the shutter member to nove rightwardsand close off passageway 62.

A (non-illustrated) source of biasing pressure, here it a value of 1.4kg/cm has an outlet 63 which in turn ias two branches 63 and 63" whichlead into two inets of the minimum pressure detector 6. the branch 63eads into a chamber 64. The chamber 64 is bounded )n the left side by awall through which passes the aforementioned passageway 62. The chamber64 is )ounded on the right side by a flexible diaphragm 65 which isoperative, when urged in rightwards direction, "or moving a sphericalvalve member 66 in rightwards direction. It will be noted that, whenshutter member 61 has not closed off passageway 62, pressure will not beable to build up in chamber 64, by reason of the communication ofchamber 64 with the atmosphere, via passage 62 and outlet 68. Thus, whenpassage 62 is open, the pressure in chamber 64 will not build up to anextent sufficient to push diaphragm 65 in rightwards direction andthereby push spherical valve member 66 to its rightmost position. On thecontrary, the spherical valve member 66 will be pushed to itsillustrated leftmost position, under the action of the pressure inconduit 63".

Inlet conduit 63" communicates with outlet conduit 67, and whenspherical valve member 66 is in the illustrated leftmost positionthereof, the 1.4 kg/cm pressure in conduit 63" will be transmitted tooutlet conduit 67.

It follows from what has been said that a pressure of 1.4 kg/cm willappear in conduit 67 in the event that the pressure in compartment 53,Le, the pressure in the patients lungs during the inhalation phase a orduring the pause b, falls below a predetermined minimum value. So longas the pressure in the patients lungs is above the preselected minimumvalue, no 1.4 kg/cm pressure signal will appear in conduit 67.

The conduit 67 leads into a compartment 76 of a pneumatic bistabledevice 7. The bistable device 7 is comprised of a housing having twoprincipal inlets 71 and 72 and a cylindrical valve member 73 suspendedby three flexible diaphragms 74, 74', 74" for movement between uppermostand lowermost positions closing off one or the other of the inlets 71,72. The flexible diaphragms 74, 74, 74" divide the interior of thedevice 7 into four compartments 75, 76, 77, 78. It will be noted thatthe area of the diaphragm 74 exposed to the effects of pressure isconsiderably greater than the area of the diaphragms 74 and 74".

The inlet 71 of the chamber 75 of device 7 is connected to conduit 8. Asexplained above, there appears on conduit 8 the 200/1000 sec.synchronizing pulse synchronized with the pause b between the inhalationphase and the exhalation phase.

A biasing-pressure conduit 11 leads into the compartment 77 of thebistable device 7 and establishes in compartment 77 a biasing pressureof l kg/cm", which normally maintains valve member 73 in its illustrateduppermost position. Accordingly, communication between inlet 71 andoutlet 71' will be blocked, and when the synchronizing pressure pulsesappear on synchronizing line 8 and are applied to the inlet 71 of device7, no output signal will be developed at the outlet 71' thereof.

However, in the event that the pressure in the patients lungs duringeither the inhalation period a or the pause period b falls between thepredetermined minimum value associated with the units 5 and 6, then a1.4 kg/cm pressure signal will appear on line 67 (as explained before),and this 1.4 kg/cm pressure will accordingly become established incompartment 76, overcoming the l kg/cm pressure in compartment 77 andthereby moving the valve member 73 to its lowermost position. If thevalve member 73 moves to the lowermost position during the existence ofa 1.4 kg/cm synchronizing pulse at inlet 71, then a 1.4 kg/cm outputpulse will appear at outlet 71. Clearly, this will occur only if thepressure in the patients lungs falls below the aforementioned minimumvalue during the pause period b. If the pressure in the patients lungsfalls below the predetermined minimum during the inhalation period a, nooutput pulse will appear at outlet 71 because there will be no 1.4 kg/cmsynchronizing pulse at inlet 71.

The 1 kg/cm biasing pressure established in compartment 77 is utilizedsolely to establish a biasing pressure. Accordingly, a simple biasingspring could be substituted for the use of the pressurized biasing gas.It will be understood by those skilled in the art that the 1.4 kg/cmpressure of the synchronizing pulse at inlet 71 cannot of itself movethe valve member 73 down, although it is higher than the 1 kg/cm biasingpressure, because of the small area upon which the 1.4 kg/cm pressureacts, compared to the area of diaphragm 74' upon which the l kg/cmbiasing pressure acts.

In any event, if the pressure in the patients lungs should happen to belower than the preselected minimum, and during the pause period b inparticular, then an dutput pressure pulse will appear at outlet 71' andbe transmitted by conduit 79 to inlet 92 of bistable device 9.

lncidentally, it is noted that this transmitting conduit 79 is connectedto the inlet 72 of the device 7. Accordingly, when the valve member 73of device 7 is in its illustrated position, conduit 79 communicates withthe atmosphere via inlet 72 and outlet 72, the latter being open to theatmosphere. This positively prevents the development of a pressure pulseon the output line 79 so long as the valve member 73 is in itsillustrated position.

The bistable device 9 is structurally similar to the bistable device 7described before. The device 9 is comprised of a housing having inlets91 and 92, with associated outlets 91' and 92. The device has a valvemember 83 mounted on three flexible diaphragms 84, 84,

a 84", which divide the interior of the device-9 into four compartmentsor chambers 85, 86, 87 and 88. A biasing pressure conduit 99 leads intothe compartment above diaphragm 84" and maintains that compartment at abiasing pressure of l kg/cm This biasing pressure serves to normallymaintain the valve member 83 in its illustrated uppermost position.

The inlet 91 of the device 9 is connected to a source of 1.4 kg/cmpressure, via a pressure conduit 12 and a three-port valve 43. Valve 43has a port- 14 which communicates with the atmosphere, and is providedwith a pushbutton 43'. Normally, the pressure in conduit 12 iscommunicated to inlet 91. However, when pushbutton 43' is pressed, theposition of the valveis changed, so as the conduit 12 is closed and theinlet 91 is communicated to the atmos'pere.

It will be understood that, normally, valve member 83 maintains itsillustrated position despite the greater pressure at its upper surfacethan at the supporting diaphragm 84, because the 1.4 kg/cm acts upon alesser surface area than the 1 kg/cm biasing pressure.

Now, if the 1.4 kg/cm' pressure pulse discussed above appears on theconduit 79, and is established in the compartment 88, the pressure inoutlet 92' will rise to 1.4 kg/cm and will be transmitted via conduit 15to an alarm system 10, comprised in this embodiment of a light bulb anda horn. The light bulb and horn may be provided with pressure-responsiveelectrical switches and may be electrically operated.

Moreover, a self-locking action occurs. Specifically, the 1.4 kg/cmpressure in line 15 is communicated not only to the warning system 10,but also to the compartment 86 of the device 9. The 1.4 kg/cm pressurein compartment 86 overcomes the l kg/cm biasing pressure in thecompartment immediately below, and the valve member 83 moves downwardly.As a result, 1.4 kg/em pressure is established in compartment 85. Sincethe outlet 91' of compartment 85 communicates with the compartment 86immediately below, the 1.4 kg/cm pressure in compartment 85 will bemaintained in compartment 86 immediately below, even in the event thatthe 1.4 ltg/cm pressure pulse on line 79 terminates, which of course itwill at the end of the pause period b.

The energization of the alarm and the warning light will summonpersonnel to the installation to correct the malfunction or otherdifficulty. During this time it may be desired to terminate the warningsignals, and for this purpose the pushbutton 43 is provided. Whenpushbutton 43' is depressed the 1.4 kg/cm pressure in the inlet 91 isdiverted to exhaust port 14, thereby terminating the self-locking actionjust mentioned.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types oflogic circuits and constructions differing from the types describedabove.

While the invention has been illustrated and described as embodied in anarrangement for monitoring the operation of an artificial respirationmachine, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention. The sameapparatus described in connection with FIGS. 1 to 5 can be used for thecontrol of the pressure into the patients lungs and in the pause b toavoid that said pressure overcomes the maximum pressure value dangerousfor the patient, only by inverting the connections of pipes 11 and 67 tothe device 7.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. An artificial respiration system comprising, in combination,respirating means for alternately forcing air into the lungs of apatient during an inhalation period and permitting outflow of air fromthe lungs of the patient during a subsequent exhalation period;synchronizing means for generating a synchronizing signal indicative ofthe time intermediate said inhalation period and said exhalation period;warning means for issuing a warning signal; pressure-detecting means fordetecting when the pressure of air in the lungs of the patient fallsbelow a predetermined value; and activating means connected to saidsynchronizing means for receipt of said synchronizing signal andconnected to said pressure-detecting means and operative for causingsaid warning means to issue a warning signal if the pressure detected bysaid pressure-detecting means falls below said predetermined valueduring the time of receipt by said activating means of saidsynchronizing signal.

2. The system defined in claim 1, wherein said synchronizing meanscomprises control means connected to said respirating means forcontrolling the sequence of operation of the same and operative forgenerating a first signal to cause said respirating means to force airinto the lungs of the patient and operative for generating a secondsignal to cause said respirating means to permit outflow of air from thelungs of the patient and operative for generating said synchronizingsignal intermediate said first and second signals.

3. The system defined in claim 1, wherein said respirating meanscomprises inhalation conduit means for carrying air into the lungs ofthe patient and a source of ventilation gas connected to said inhalationconduit means at one end of said inhalation conduit means and operativefor establishing a predetermined pressure in said inhalation conduitmeans, and exhalation conduit means for carrying air out of the lungs ofthe patient, valve means for selectively establishing communicationbetween the lungs of the patient and either said inhalation conduitmeans or said exhalation conduit means, said pressure-detecting meanscomprising means for detecting when the pressure of air in saidinhalation conduit means falls below a predetermined value, and whereinsaid synchronizing means comprises control means connected to saidrespirating means for controlling the sequence of operation of the sameand operative for generating a first signal to cause said valve means toestablish communication between said inhalation conduit means and thelungs of the patient and cause said source to establish saidpredetermined pressure in said inhalation conduit means and operativefor generating a second signal to cause said valve means to establishcommunication between said exhalation conduit means and the lungs of thepatient and operative for generating said synchronizing signalintermediate said first and second signals to maintain communicationbetween said inhalation conduit means and the lungs of the patient andsimultaneously prevent said source from establishing said predeterminedpressure in said inhalation conduit means so that the pressureestablished in said inhalation conduit means intermediate saidinhalation and exhalation phases will be dependent upon the pressure inthe patients lungs.

4. The system defined in claim 1, wherein said pressure-detecting meanscomprises means for generating an insufficient-pressure signal when thepressure of air in the lungs of the patient falls below a predeterminedvalue, and wherein said activating means comprises an AND-gate havingone input for receipt of said synchronizing signal and having anotherinput for receipt of said insufficient-pressure signal and having anoutput connected to said warning means and being operative foractivating said warning means when an insufficientpressure signal and asynchronizing signal are concurrently present at said inputs of saidAND-gate.

5. The system defined in claim 1, wherein said activating meanscomprises manually operable means for deactivating said warning means.

6. The system defined in claim 1, wherein said activating meanscomprises bistable means operative when in one of the two states thereoffor causing said warning means to generate a warning signal andoperative when in the other of the two states thereof for maintainingsaid warning means non-activated, and means for triggering said bistablemeans into said other of the two states thereof if the pressure detectedby said pressuredetecting means falls below said predetermined valueduring the time of receipt by said activating means of saidsynchronizing signal.

7. The system defined in claim 1, wherein said activating means furthercomprises manually operable means for resetting said bistable means tosaid one state thereof.

8. A method of artificial respiration, comprising, in combination, thesteps of first forcing respiration gas into the lungs of a patientduring an inhalation period, then during a subsequent pause periodterminating the forcing of air into the patients lungs but withoutpermitting exhalation by the patient during such pause period, and thenpermitting outflow of air from the patients lungs during a subsequentexhalation period; generating synchronizing signals during the pauseperiods; and generating a warning signal if the gas pressure in thepatients lungs falls below a predetermined value during generation ofone of the synchronizing signals.

9. The method defined in claim 8, wherein said step of generating awarning signal comprises generating a warning signal if and only if thegas pressure in the patients lungs falls below a predetermined fixedvalue during generation of one of the synchronizing signals.

1. An artificial respiration system comprising, in combination,respirating means for alternately forcing air into the lungs of apatient during an inhalation period and permitting outflow of air fromthe lungs of the patient during a subsequent exhalation period;synchronizing means for geNerating a synchronizing signal indicative ofthe time intermediate said inhalation period and said exhalation period;warning means for issuing a warning signal; pressure-detecting means fordetecting when the pressure of air in the lungs of the patient fallsbelow a predetermined value; and activating means connected to saidsynchronizing means for receipt of said synchronizing signal andconnected to said pressure-detecting means and operative for causingsaid warning means to issue a warning signal if the pressure detected bysaid pressure-detecting means falls below said predetermined valueduring the time of receipt by said activating means of saidsynchronizing signal.
 2. The system defined in claim 1, wherein saidsynchronizing means comprises control means connected to saidrespirating means for controlling the sequence of operation of the sameand operative for generating a first signal to cause said respiratingmeans to force air into the lungs of the patient and operative forgenerating a second signal to cause said respirating means to permitoutflow of air from the lungs of the patient and operative forgenerating said synchronizing signal intermediate said first and secondsignals.
 3. The system defined in claim 1, wherein said respiratingmeans comprises inhalation conduit means for carrying air into the lungsof the patient and a source of ventilation gas connected to saidinhalation conduit means at one end of said inhalation conduit means andoperative for establishing a predetermined pressure in said inhalationconduit means, and exhalation conduit means for carrying air out of thelungs of the patient, valve means for selectively establishingcommunication between the lungs of the patient and either saidinhalation conduit means or said exhalation conduit means, saidpressure-detecting means comprising means for detecting when thepressure of air in said inhalation conduit means falls below apredetermined value, and wherein said synchronizing means comprisescontrol means connected to said respirating means for controlling thesequence of operation of the same and operative for generating a firstsignal to cause said valve means to establish communication between saidinhalation conduit means and the lungs of the patient and cause saidsource to establish said predetermined pressure in said inhalationconduit means and operative for generating a second signal to cause saidvalve means to establish communication between said exhalation conduitmeans and the lungs of the patient and operative for generating saidsynchronizing signal intermediate said first and second signals tomaintain communication between said inhalation conduit means and thelungs of the patient and simultaneously prevent said source fromestablishing said predetermined pressure in said inhalation conduitmeans so that the pressure established in said inhalation conduit meansintermediate said inhalation and exhalation phases will be dependentupon the pressure in the patient''s lungs.
 4. The system defined inclaim 1, wherein said pressure-detecting means comprises means forgenerating an insufficient-pressure signal when the pressure of air inthe lungs of the patient falls below a predetermined value, and whereinsaid activating means comprises an AND-gate having one input for receiptof said synchronizing signal and having another input for receipt ofsaid insufficient-pressure signal and having an output connected to saidwarning means and being operative for activating said warning means whenan insufficient-pressure signal and a synchronizing signal areconcurrently present at said inputs of said AND-gate.
 5. The systemdefined in claim 1, wherein said activating means comprises manuallyoperable means for deactivating said warning means.
 6. The systemdefined in claim 1, wherein said activating means comprises bistablemeans operative when in one of the two states thereof for causing saidwarning means to generate a warning signal and operativE when in theother of the two states thereof for maintaining said warning meansnon-activated, and means for triggering said bistable means into saidother of the two states thereof if the pressure detected by saidpressure-detecting means falls below said predetermined value during thetime of receipt by said activating means of said synchronizing signal.7. The system defined in claim 1, wherein said activating means furthercomprises manually operable means for resetting said bistable means tosaid one state thereof.
 8. A method of artificial respiration,comprising, in combination, the steps of first forcing respiration gasinto the lungs of a patient during an inhalation period, then during asubsequent pause period terminating the forcing of air into thepatient''s lungs but without permitting exhalation by the patient duringsuch pause period, and then permitting outflow of air from thepatient''s lungs during a subsequent exhalation period; generatingsynchronizing signals during the pause periods; and generating a warningsignal if the gas pressure in the patient''s lungs falls below apredetermined value during generation of one of the synchronizingsignals.
 9. The method defined in claim 8, wherein said step ofgenerating a warning signal comprises generating a warning signal if andonly if the gas pressure in the patient''s lungs falls below apredetermined fixed value during generation of one of the synchronizingsignals.